1. Technical Field
The present invention relates to a light filter, a manufacturing method of the light filter, and an optical device.
2. Related Art
In related art, for example, as disclosed in Patent Document 1 (JP-A-2009-134028), a light filter including a Fabry-Perot etalon filter having a pair of optical films opposed via a predetermined gap (hereinafter, may be referred to as “etalon filter”, or simply as “etalon”) is known.
The etalon filter described in Patent Document 1 has a first substrate and a second substrate held in parallel to each other, a first optical film (first reflection film) formed on the first substrate, and a second optical film (second reflection film) formed on the second substrate and opposed to the first optical film with a predetermined gap. The respective first optical film and second optical film form mirrors and may transmit only light in a predetermined wavelength range in response to the length of the gap (the amount of the gap) by multiple interference of light between the mirrors. Further, by variably controlling the amount of the gap, the wavelength range of light to be transmitted through may be shifted.
Furthermore, in the etalon filter described in Patent Document 1, bonding films containing a siloxane (Si—O) bind are used for bonding between the first substrate and the second substrate. The accuracy of wavelength separation in the etalon filter has a deep relationship with the accuracy of the amount of the gap. Therefore, to improve performance and quality of the etalon filter, it is necessary to control the length of the gap between the first optical film and the second optical film with stability and high accuracy.
However, in the etalon filter described in Patent Document 1, for bonding the respective substrates using the bonding films, for example, it is necessary to activate the bonding films formed on the respective substrates by ultraviolet radiation, oxygen plasma treatment, or the like, perform alignment of the respective substrates, and then, apply loads on the respective substrates, and the substrates may be slightly slanted and parallelism of the optical films may be difficult to be ensured at these steps.
As a cause of slanting of the substrates, for example, there is misalignment when the bonding films are partially formed on the respective substrates (bonding film misalignment) and substrate misalignment at the step of bonding the respective substrates to each other. Further, inclination, rounding, or the like is easily formed in the edge parts of the bonding films, and this also causes the slanting of the substrates.
For the slanting of the substrates, the applicant has tried to ensure the parallelism between the optical films provided on the respective substrates by forming the bonding films on the entire surfaces of the substrates and suppressing the slanting of the substrates, and has achieved some positive results.
However, damage may occur on the bonding films at the post process of forming and patterning electrodes and optical films for variable control of the amount of the gap, and gap stability between the optical films may not be ensured. That is, there has been a problem that it is difficult to constantly ensure stable quality. It has been estimated that the cause of the damage of the bonding films is that, after formation of the bonding films, patterning is respectively performed for forming the electrodes and the optical films.